I agree with John, the T-Stat should be changed. The wattage of the element is irrelevant as this T-Stat switch should remain 'ON' unless and until there is a 'Fault' condition that triggers its activation. Until then it should behave as if it were a straight piece of wire.

The switching occurs in the Solid State Relay (SSR), (controlled by the PID) and due to the nature of an SSR, there should be no Arcing or Sparking; that would occur in a mechanical relay, which is in part the reason for the shift away from mechanical relays to SSR.

The 'Transient' you are experiencing in your T-Stat is due to carbon deposits on its contacts when current is switched 'ON' and possibly even 'OFF'. Were this T-Stat functioning 'Normally' there would be no transient in the T-Stat, as it would be behaving as a straight piece of wire until its spec'd upper temperature limit is exceeded.

BTW: Just for me, on my own machine, I would still install that .01mfd/1000v Ceramic Disk Capacitor access the T-Stat leads.

On one hand, I agree with thought/theory of the safety thermostat self-tripping: carbon deposits, in theory, could increase internal resistance, causing transient currents and, in turn, excessive heat causing the t-stat to trip. Fine. On the other hand, this is the 3RD t-stat in this 2017 machine!
Statistically, I'd expect to see posts all over the place with users complaining about their t-stats tripping left-and-right, with Scott @ LM offering LMLM buyers an annual t-stat subscription
I have a different theory and I'm now testing it: I think that the PID is going haywire due to a bad signal/sensor - but only while initially warming up. If I'm right, then adding a non-latching, lower-temp t-stat inline with the safety one, should add some tolerance to the system - without impacting its safety. If the PID has a few "moments of confusion" when starting, the temp t-stat will keep the system well below the safety threshold, avoiding an unnecessary safety trip (and the annoying manual reset required for it).

So that's what I did exactly. The LM espresso boiler happens to have a few unused, pre-drilled M3 holes, nicely spaced for extra t-stats (perhaps to accommodate machines with no PIDs?) - I installed (one of these 110C t-stats) and connected it to the original safety t-stat with a heat-resistant wire. This mod is quick, easy, cheap and completely reversible. If the root cause is carbon deposits, like you guys think, then this mod will not help and the safety t-stat should keep tripping. If it is indeed the PID/sensor, then I should never see it tripping again...

vansover wrote:@Alestz - any updates? Looks like almost 4 months passed since February - was the temp probe indeed replaced? Did the issue of the safety switch triggering disappear/get resolved?

I'm trying to troubleshoot what seems to be the same issue. The thermal switch on my LMLM trips occasionally - when it does, it happens only when turning the machine on. It never tripped for me if the machine is already at operating temperature.

Scott tried to assist me as well. We replaced the PID's potentiometer, replaced the safety switch (twice), upgraded the control module to the "connected" version - nothing helped

Hey - sorry, I completely forgot about this thread... It turns out that replacing the temp probe did fix it! Been using the LMLM daily for the past 4 months or so with 0 issues

The issue that I had sounds a bit different. When the thermal switch tripped, it was only after the machine was warmed up for a hour or longer and not immediately after turning the machine on

vansover wrote:On one hand, I agree with thought/theory of the safety thermostat self-tripping: carbon deposits, in theory, could increase internal resistance, causing transient currents and, in turn, excessive heat causing the t-stat to trip. Fine. On the other hand, this is the 3RD t-stat in this 2017 machine!
Statistically, I'd expect to see posts all over the place with users complaining about their t-stats tripping left-and-right, with Scott @ LM offering LMLM buyers an annual t-stat subscription
I have a different theory and I'm now testing it: I think that the PID is going haywire due to a bad signal/sensor - but only while initially warming up. If I'm right, then adding a non-latching, lower-temp t-stat inline with the safety one, should add some tolerance to the system - without impacting its safety. If the PID has a few "moments of confusion" when starting, the temp t-stat will keep the system well below the safety threshold, avoiding an unnecessary safety trip (and the annoying manual reset required for it).

So that's what I did exactly. The LM espresso boiler happens to have a few unused, pre-drilled M3 holes, nicely spaced for extra t-stats (perhaps to accommodate machines with no PIDs?) - I installed (one of these 110C t-stats) and connected it to the original safety t-stat with a heat-resistant wire. This mod is quick, easy, cheap and completely reversible. If the root cause is carbon deposits, like you guys think, then this mod will not help and the safety t-stat should keep tripping. If it is indeed the PID/sensor, then I should never see it tripping again...

Interesting theory, interesting mod; perhaps this might help someone in the future.

Thanks for posting that.

Alestz wrote:Hey - sorry, I completely forgot about this thread... It turns out that replacing the temp probe did fix it! Been using the LMLM daily for the past 4 months or so with 0 issues

The issue that I had sounds a bit different. When the thermal switch tripped, it was only after the machine was warmed up for a hour or longer and not immediately after turning the machine on

Glad you got your problem resolved. Keep us posted if anything changes.

Good Luck!

Alestz wrote: It turns out that replacing the temp probe did fix it! Been using the LMLM daily for the past 4 months or so with 0 issues

Thanks for this update - very useful. And best of luck - I hope your LMLM keeps operating well for many years.
As to the faulty probe - if my machine also "suffers" from the same issue, then my "110C mod" may not solve it, but should be able to "hide" the issue.
I'll report back in a few months.

3-week update on the 110C pre-safety thermostat mode. This morning I "caught" the 110C t-stat "tripping."

The PID light was still blinking, indicating the boiler's temp cannot be stabilized by the PID (of course, it was around 110C, instead of its set 93C).
The mod was successful. It (1) prevented the real safety t-stat from tripping, and manually letting some (hot) water out the brew head cooled the boiler, reset the 110C t-stat and let the PID take over and back to normal operation. So no need to open the machine the reset the safety. The mod also (2) proved that the issue is unlikely related to a fault in the safety t-stat (like carbon buildout).

What I've seen is a situation where the boiler's temp is clearly out of bounds, yet the PID is still sending "heating pulses." This likely indicates my machine is suffering from the same issue Alestz's machine was plagued with: a faulty temp probe.

I took a look, and...not sure a temp probe replacement on a LMLM is an easy DIY job. I think this will need a pro. Luckily, with the mod, I don't have to be in a hurry...

Root cause found - I did a sloppy job a couple of years ago with the "barista lights" mod. I thought I was only affecting the LEDs on the Linea Mini, but it turns out that the brew boiler's temp sensor is somehow "riding" on the same wires (or, rather, the LEDs are "riding" on the temp sensor wires).
Chris from La Marzocco gave me the hint. I was asking him for shop recommendations, to take my machine in and get the temp sensor replaced, as @Alestz did. Chris said it is unlikely that a temp sensor would be flaky - in his experience, these sensors either work or fail completely.
Once I fixed my sloppy "LED" wiring job, the overheating stopped occurring.